Harrows have been used by farmers to assist in preparation of soil for farming. This can include breaking up the soil, furrowing it, and depositing the broken up material into the ground. It may also include uprooting and breaking stubble from the previous harvest or other plant material, such as weeds.
It is known to provide harrows that include a plurality of discs (harrow members) linked together to form a chain. The chain is pulled along the ground surface whereby the discs roll and engage the ground to break the soil and other material therein. Typically, the surfaces of the discs are at an angle to the direction of travel to provide an angle of attack between the discs and the soil.
Such harrows can be mechanised, with the chain of discs extending between two sides of a frame, with the frame towed by a tractor or other farm equipment. Such a known type of harrow is described in Australian patent no. 2007216912. In this prior art, each link in the chain includes a harrow disc, and a pair of link portions, such as a hook portion and a loop portion, disposed on either side of the harrow disc. To form the chain, the hook is hooked into the loop of an adjacent link, and the chain is tensioned to prevent the links from unhooking and separating. To separate the links, tension is relaxed so the links can be unhooked.
Known systems, such as that described in AU 2007216912 have a chain formed of links where the hook, loop and disc are all integral. For example having the disc, hook portions, and loop portions welded together. In another form, the hook, loop, and disc of a link may be formed by a single casting, forging or other integrally forming technique. This is provided to assist assembly and disassembly for the user, as one needs only to hook and unhook the links.
However where the links are integral, it may be impractical to maintain or repair individual links that are worn or damaged. For example, if a hook portion is broken or damaged, the whole link may need to be discarded even if the loop portion and the harrow disc is still serviceable. Similarly, if the harrow disc is worn or damaged during use, the link may need to be discarded even if the loop portion and hook portion are serviceable.
Furthermore, integral links may result in limitations on methods of manufacture and material properties of the link. It may also lead to a compromise of the required properties of the disc and the materials. For example, the loop and hook portion has a primary function of joining the link together, whereas the harrow disc has the function of impacting with and engaging earth. Thus the harrow disc may wear at a rate much higher than the hook loop and require higher wear resistance and toughness/hardness than the other portions. Thus an integral link or integrally formed link may include a compromise in material properties. There may also be financial costs, as portions of the link may consequently be made of materials or formed by a process that is beyond the practical requirements.
As an example, it is known to manufacture a link with the harrow disc, loop portion, and hook portion in a single casting. Casting a component can produce a weaker component compared to other (and usually more expensive) techniques. As a result, to obtain an acceptable strength for the harrow disc, an integrally formed link made from casting may require the harrow disc to be thicker and heavier compared to, for example only, a forged harrow disc. However, for technical and financial reasons, it may be acceptable for the loop and hook portions to be formed of casting.
Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.